The present invention concerns an injection system of an internal combustion engine and an automotive vehicle including such an injection system.
Common rail fuel injection systems are used in most of diesel engines, from passenger cars to large heavy duty engines. The injection rate of these injection systems, i.e. the instantaneous injected flow curve, has a fixed profile as the available pressure in the injector during an injection is considered almost constant. However, a slow and progressive delivery of fuel at the very start of the main injection can be beneficial to decrease gases emissions, for example NOx emissions, in the first phase of the combustion.
Besides that, if the opening phase is too slow, it can lead to too long injection durations, which implies loss of combustion efficiency or problems due to too late end of injection, or instable injector opening and poor control of the total fuel injected quantity. Thus, it can be advantageous to reach full needle opening and spray formation on most of engine operating points.
DE-A-197 40 997 discloses an injection system having a control valve controlled by a solenoid. When the solenoid is not supplied with electric power, the control valve is urged downwards by a spring in order for injector to rise in an open position, against the return force of a second spring. When electrical power is supplied to the solenoid, the control valve is lifted in an open position at a low lift speed. During the lift of the needle, an additional fuel path is opened, which leads to an acceleration of the lift of the needle, so the speed of the fuel flow gets higher. Opening of the additional fuel path is controlled by the position of the needle. In this way, during the injector opening, the infection rate has two slopes. However, such an arrangement is not favorable for the needle movement control, which is expected to be free from side loads in order to avoid problems of poor spray symmetry, poor needle movement consistency and accelerated wear.
It is desirable to provide an injection system enabling to have two slopes of the injection rate during the injector opening, offering the option to tune the profile in terms of slope and duration in the opening phase, thanks to the selection of the right hardware features.
It is also desirable to keep an independent control of the injection closure velocity, as this feature is known to influence pollutant formation at the end of the combustion process.
It is also desirable to provide an injection system having a limited cost, a reduced size and complexity, in particular with the intention to keep an injector design with a single electronically controlled valve.
According to a first aspect of the invention, a fuel injection system of an internal combustion engine is provided, comprising:                an injector having a hydraulic control chamber controlling the delivery of fuel through the injector,        an actively controlled first valve system controlling the pressure relief from the control chamber, the first valve system being movable between:        a first position in which the first valve system closes the injector by deterring the pressure from being relieved from the control chamber through the first relief circuit, and        a second position in which the first valve system opens the injector by allowing the pressure to be relieved from the control chamber through the first relief circuit.        
The fuel injection system comprises a second relief circuit allowing the pressure to be relieved from the control chamber. The second relief circuit comprises a second valve system having a control port passively controlled by the fuel pressure and movable between:                a first position in which the second valve system deters the pressure from being relieved from the control chamber through the second relief circuit and        a second position in which the second valve system allows the pressure to be relieved from the control chamber through the second relief circuit.        
By the provision of an injection system which comprises a passive valve movable depending on the pressure in the chamber, the injection system is safe, has a limited cost, and a reduced size and complexity.
The system may comprise also one or several of the following features:                the first valve system may include a first directional control valve having a first port designed to be connected to a high pressure fuel source;        the first relief circuit may include a first relief line having a first flow resistance for controlling the flow rate of the fuel relieved from the control chamber.        during a first injection phase in which the pressure is relieved from the control chamber through the first relief circuit and in which the second valve system deters the pressure from being relieved from the control chamber through the second relief circuit, a first speed of increase of the injection rate may be determined by the first flow resistance.        the second relief circuit may include a second relief line having a second flow resistance for controlling the flow rate of the fuel relieved from the control chamber (12);        in a second injection phase in which pressure is relieved from the control chamber through the second relief circuit, a second speed of increase of the injection rate is determined.        the second speed of increase may be higher than the first speed of increase.        the control port of the second valve system may be connected to:        an opening control line having a flow resistance, for adjusting the timing between the first injection phase and the second injection phase,        a closing control line having a smaller flow resistance than the opening control line and a equipped with a check valve preventing flow of fuel from the control port of the second valve system.        
This allows asymmetrical time responses between opening and closing of the second valve system.                the first valve system may include a first directional control valve electromagnetically controlled by an electronic control unit.        the first valve system may include a mechanical return device for returning the first valve system in the first position.        the second valve system may include mechanical return means for returning the second valve system in the first position.        the injection system may include a third flow restrictor for adjusting the closing speed of the injector.        the injection system may include:        a pressure feed line for feeding the control chamber with pressurized fuel, said pressure feed line being equipped with a first check valve preventing flow of fuel from the control chamber, and        a first relief line, in parallel to the pressure feed line and having a first flow resistance, for relieving fuel from the control chamber though the first valve system.        the third flow restrictor for adjusting the closing speed of the injector may be located in the pressure feed line.        the system may include a needle and the pressure in the control chamber may control the position of the needle and the delivery of fuel through nozzles.        when the pressure in the control chamber is above a pressure threshold, the needle closes the nozzles and in that when the pressure in the control chamber is below the pressure threshold, the needle opens the nozzles.        the injector system may include a mechanical return device applying a closing force to the needle for maintaining the needle in the closed position.        the first valve system and the second valve system may be integrated in a common body part and the needle is disposed in a pressure chamber having nozzles for fuel delivery, the pressure chamber being located inside the body part.        the needle may be movable in a pressure chamber by means of the difference in pressure between the control chamber and the pressure chamber.        in the first position of the first valve system the pressure may be delivered to the control chamber through the first valve system.        
According to a second aspect of the invention, an automotive vehicle including such a fuel injection system is provided.